baobab is an implementation of FPTrees or Frequent Pattern Trees, a pattern recognition/data mining technique. it has innumerable applications in language processing, clickstream analysis, etc.
certainly a recommended application which I've found comes HEAVILY in handy when archiving, and generally wrapping my head around what each drive contains, and where on the cylinders the folders/files are. I do graphics, video, and music on several computers so this is a god send for me. I can imagine it would be heavily useful for anybody with large amounts of any data.